The present invention relates to plasma sputtering, and more particularly, to methods and devices for forming a layer of material onto a substrate during the fabrication of semiconductor devices.
A number of semiconductor device fabrication procedures include processes in which a material is sputtered from a target onto a workpiece such as a semiconductor wafer. Material is sputtered from the target, which is appropriately biased, by the impact of ions created in the vicinity of the target. A certain proportion of the sputtered material may be ionized by a plasma such that the resulting ions can be attracted to the wafer. The wafer is mounted on a support and is usually biased to a DC potential selected to attract the sputtered, ionized material. Typically, the sputtered material is composed of positive ions and the workpiece is negatively biased.
Sputtered material has a tendency to travel in straight line paths from the target to the substrate at angles which are oblique to the surface of the substrate. As a consequence, high aspect ratio (depth to width) features such as trenches and holes on a substrate surface may not be completely filled during deposition because deposition material may build up near the top edges of the high aspect ratio feature and close off a void or cavity. To inhibit the formation of such cavities, the sputtered material can be redirected into substantially vertical paths between the target and the substrate by negatively charging the substrate and positioning appropriate vertically oriented electric fields adjacent the substrate if the sputtered material is sufficiently ionized by the plasma. However, material sputtered by a low density plasma often has an ionization degree of less than 10%, which is usually insufficient to avoid the formation of an excessive number of cavities. Accordingly, it is desirable to increase the density of the plasma to increase the ionization rate of the sputtered material in order to decrease the formation of unwanted cavities in the deposition layer.
There are a variety of known techniques for exciting a plasma with RF fields including capacitive coupling, inductive coupling and wave heating. In a standard inductively coupled plasma (ICP) generator, RF current passing through a coil surrounding the plasma induces electromagnetic currents in the plasma. These currents heat the conducting plasma by ohmic heating, so that it is sustained in steady state. As shown in U.S. Pat. No. 4,362,632, for example, current through a coil is supplied by an RF generator coupled to the coil through an impedance matching network, such that the coil acts as the first windings of a transformer. The plasma acts as a single turn second winding of a transformer.
In many high density plasma applications, it is preferable for the chamber to be operated at a relatively high pressure so that the frequency of collisions between the plasma ions and the deposition material atoms is increased to thereby increase the time that the sputtered material remains in the high density plasma zone. However, scattering of the deposition atoms is likewise increased. This scattering of the deposition atoms typically causes the thickness of the deposition layer on the substrate to be thicker on that portion of the substrate aligned with the center of the target and thinner in the outlying regions.
It has been found that the deposition layer can be made more uniform by reducing the distance between the target and the substrate, which reduces the effect of the plasma scattering. On the other hand, in order to increase the plasma density to increase the ionization of the sputtered atoms, it has been found desirable to increase the distance between the target and the substrate. The coil which may be used to couple energy into the plasma typically encircles the space between the target and the substrate. If the target is positioned too closely to the substrate, the ionization of the plasma can be adversely affected. Thus, in order to accommodate the coil, it has often been found necessary to space the target from the substrate a certain minimum distance even though such a minimum spacing can have an adverse effect on the uniformity of the deposition.
Certain embodiments of the present invention relate to improved devices and methods for sputtering depositing a layer onto a workpiece which overcome the above-mentioned limitations.
In certain embodiments a body is placed within a deposition chamber between the target and the workpiece. This body acts to control the deposition profile by inhibiting material from being sputtered from the target onto a portion of the workpiece. Other embodiments control the size and shape of the target sputtering region to yield a desired deposition profile on the workpiece.
One embodiment for sputtering material onto a workpiece in a chamber includes a plasma generation area and a target. A coil is positioned to inductively couple energy into the plasma generation area to generate and sustain a plasma. A body is positioned on or adjacent to the target to prevent an amount of target material from being sputtered onto the workpiece. In certain embodiments the target includes a center region and an outer region and the body prevents an amount of target material from the center region from being sputtered onto the workpiece. The body may act as a physical shield to block sputtered material from accumulating on the workpiece. The body may also act as a dark space shield and inhibit plasma formation between the body and the target, thus inhibiting sputtering over a portion of the target.
Other embodiments for sputtering a material onto a workpiece include a chamber having a plasma generation area and a ring-shaped target material surrounding a center mass. The center mass and ring-shaped target material are electrically isolated from one another. An energy source is provided for coupling energy into the plasma generation area to generate and sustain a plasma. Sputtering the ring-shaped target material can in certain embodiments provide for a more uniform deposition layer.
Another embodiment relates to a method for sputtering a layer onto a workpiece including sputtering at least a portion of a target and positioning a body adjacent to a central portion of the target and between the target and the workpiece to inhibit material from the central portion of the target from being deposited on the workpiece.
Yet another embodiment relates to a target structure including a ring-shaped region and a central region surrounded by the ring-shaped region. The regions are coupled together in a manner in which the ring shaped-target region is electrically isolated from the center region. In certain embodiments the central region may be electrically grounded to inhibit sputtering of material from the central region.